Cover Crops for Better Soil

During the 1930s the Southern Plains region of the country was in the grips of a severe drought that led to the term “Dust Bowl.”

Unplanted farmlands became wind-blown deserts as crops failed and livestock was killed by the unrelenting heat, drought and loss of vegetation. One of the contributing factors was the mismanagement of farmland and rangeland by both the government and farmers. However, one of the solutions was in both government and farmers. And home gardeners can learn from this no matter the size of your garden or fields.

In 1934 the dust storms were so bad that ships in New York Harbor were coated with the dust blown from the Midwest, as was the Statue of Liberty. I can only imagine what happened to outdoor ornamentals and gardens. Just think back to the smoke from last year and add days and days of dust to it.

One of the things that went wrong was the constant tilling of the soil, harvesting of the crops then doing nothing to keep the soil in place. Add persistent drought, some wind, and you’ve got the makings for what was called the “Black Blizzard.”

What followed and what continues was and is the practice of adding cover crops to soils that aren’t in use for crop production. The government made major changes requiring farms getting federal aid and subsidies to plant cover crops, and to this day cover crops are required in some areas to stabilize the soil.

In 2019 Amagansett had its own dust storm. In January of that year dust-covered cars and parking lots were seen in the Town of East Hampton where potato farmers left their harvested fields unplanted. It got very dry and very windy that December and January, and a local dust storm ensued. As a result, the town required farmers to be proactive in stabilizing their soils in harvested fields for the winter months and the local zoning code was changed to affect this change. Now, farm fields are required to have a cover crop in place from December 1 through March 1.

The right cover crops — often also referred to as “green manures” — do more than just hold the soil in place, and that’s where they come in handy for our gardens, both ornamental and vegetable. A cover crop will keep your soil in place during wind and heavy rain. But with the right choices it will also add organic material to your sandy soil as well as increasing biological activity that may not be found in our sandy soils but is critical to the soil food web. This in turn will allow your sandy soil to absorb and retain more water during the growing season.

Yes, we work on a much smaller scale on our home plots, but keeping our soil in place and keeping it healthy or making it healthier is a simple way to benefit our local ecology as well as your own plots of soil.

Some of these cover crops are quick shots that can be planted and worked into the soil in just a month. On the other hand, there are those cover crops that get sown in late summer and are left in place until the following spring when they are turned under prior to planting. Here are eight crops you can try but make sure you use the right one for the right situation.

Winter rye is one of the crops that can be used and is actually No. 9. It’s planted in late summer or early fall. It’s not used that much these days because some ecologists see it as potentially invasive, but, if cut and tilled in early spring it can be easily controlled. Don’t make the mistake of using perennial rye, the turf type, or you’ll regret it for years.

White clover (Ttrifolium repens) is familiar to most of you and shows up in many of our lawns. Unlike some other cover crops, this clover is nitrogen fixing. This means it adds nitrogen to the soil instead of using it up like our lawns do. It also attracts a few pollinators when in flower. Two ounces will seed 125 square feet, and a pound will cover 2,000 square feet. Spring and late summer are the best time for sowing.

Crimson clover (Trifolium incarnatum) is also a nitrogen fixer with attractive red flowers. It can be sown early in the spring then mowed and has the advantage of crowding out many varieties of germinating weeds due to its dense growth. It can also be sown in the fall where you get growth for several months before it goes dormant then returns in the spring unless you till it. Mow it first, then turn it back into the ground — also known as a green manure. Seeding rate is the same as for white clover.

Another clover is medium red clover (Trifolium pratense) which can put 100 pounds of nitrogen back into every acre it’s grown on as it builds the soil structure at the same time. It also draws nutrients from deep in the soil, putting these nutrients closer to the surface where vegetables and garden plants can use them. Till in the spring and seed at the rate of 1/8 pound per 250 square feet.

Buckwheat is a quick-growing annual that’s great for choking out weeds and adding lots of organic matter. It can be sown any time during the growing season and cut then tilled into the garden or can be fall sown and allowed to die back during the winter, tilling it in in the spring. To rejuvenate your garden soil, make several sowings during the growing season. Cut it back just as it flowers, till in, then reseed. If you do this three times — or more — during the season your soil will be quite good the following year. Sow at the rate of ½ pound per 250 square feet.

The combination of oats and field peas is popular among farmers because the peas add lots of nitrogen to the soil and the oats stabilize the soil as well as adding structure when tilled in. This mix prefers the cooler sowing times of the spring and late summer into early fall. The pea seeds need to be under the soil to germinate while the oats can just be sown on the top and scratched in.

Hairy vetch is great for a soil stabilizer and nitrogen producer. In fact, it’s said to be one of the best nitrogen producers of the cover crops. It creates great mats of sprawling vines and should be mowed just as it begins to flower to ensure that the plants die before going to seed. The residue acts as a natural mulch if not tilled into the soil. For soil stabilization over winter, sow in late September and it will push lush growth in the spring. Then mow it before it sets seed. One-quarter pound covers 300 square feet.

Tillage radish is a new one for me and probably most readers as well. If you happen to have a clay soil — as does happen in some spots out here — it will break up the soil, improve the tilth and make the soil much more workable. It’s similar to the long daikon radish, forming giant roots that are killed during the winter. It needs to be sown in late summer. The roots turn to mush during the winter, leaving spaces in the heavy soil for both air and water to penetrate. Sow in mid to late September at the rate of 1/4 pound per 400 square feet.

Last on the list are field peas as a cover crop. Another great way to add nitrogen to your soil, but the plants die back in the winter — if it goes below 20 degrees — so you don’t get the soil stability ability of some of the other green manures and cover crops. In the spring, work the vines into the soil or leave them in place if you want to plant among them and use the pea residue as an organic mulch. Sowing rate is 1 pound to about 175 square feet.

Harvesting a garlic crop now or soon? That’s a great opportunity to get a quick cover crop in before you replant cloves in October. You’ll build your soil, add nitrogen and your garlic will love you for it. Why leave the space open for weeds? Grow a cover crop there.

Local garden centers will have a few of these cover crops, but if you want to experiment with ones you can’t find or if you want organic-certified cover crop seeds you can get them from Johnny’s and Hudson Valley Seed. Keep growing.

What Does “Nitrogen-Fixing” Mean?

You’ll often hear that certain plants, especially the family of legumes, are nitrogen fixing. But what exactly does this mean? Plants like peas, lupines, beans, vetch and clover have a biochemical relationship with the soil. These plants take nitrogen out of the air and turn it into a form that the plants can use. This is called nitrogen fixing.

When the legumes begin to decompose the residual nitrogen, which is contained on root nodules or nodes, the nitrogen becomes available to the plants. In essence, free fertilizer. In large farming operations this is why soybeans (nitrogen fixing) are sown in alternate years in fields where corn is grown. Corn needs lots of nitrogen, and the soybeans provide the nitrogen. And the beans are harvested as well. The nitrogen-containing nodules remain in the ground until the following year when the corn uses it for nutrition.

If you have very poor soil, as in extremely sandy with little organic matter, you may want to add an “inoculant” to your legume seeds. This adds needed bacteria that enhance the relationship with the legumes. This inoculant is often sold in local garden centers in small packets and online. In the vegetable garden it will also help your pea crops. Follow the directions on the packet.